Stamford High School teacher Danielle Watkins, 32, of Norwalk, was charged with two counts of sexual assault, two counts of sale of marijuana and one count of risk of injury to a minor after having an alleged affair with an 18-year-old student and providing marijuana and smoking with a second 15-year-old student, according to police.

STAMFORD -- A Stamford High School teacher accused of threatening to fail an 18-year-old student if he did not have sex with her and providing him and a friend with marijuana, turned herself over to police Wednesday.

Danielle Watkins, 32, of 11 Fort Point St., Norwalk, was charged with two counts of sexual assault, two counts of sale of marijuana and one count of risk of injury to a minor, according to a statement released by police Thursday morning.

Watkins posted $100,000 bond and is scheduled to appear in state Superior Court in Stamford on July 31.

Police launched an investigation into the allegations on June 26 after the 18-year-old student appeared at police headquarters and provided a statement about the inappropriate relationship. The victim allegedly told police that he had numerous sexual encounters with Watkins, his English teacher, from the start of the school year in September 2013 to the end in June. He told police that the encounters occurred in her car during school hours, but not on school grounds.

In addition, he told police that Watkins provided him and a friend with marijuana and they would smoke it on and off school grounds during school hours.

A day after the student reported the allegations, police executed a search warrant of Watkins's car during a motor vehicle stop in Norwalk. During the stop, police said Watkins tried to hide her cell phone under the passenger seat of the car and she became verbally combative after marijuana was discovered in the vehicle. At the time she was charged with interfering with a search warrant and possession of marijuana.

Police seized the car for a forensic examination and a search of her phone revealed over 2,000 text messages, naked pictures of herself and hundreds of calls between her and the student, police said.

"It's very upsetting, " Superintendent Winifred Hamilton said. "All our resources and support will go out to the families."

Hamilton said the teacher was suspended near the end of the year after initial reports she was acting strange with a student. The allegations were initially reported to human resources and the assistant superintendent of secondary education.

Hamilton said in about the same time frame she was contacted by a former student who knows one of the victims and more serious allegations were made.

"I immediately called the police," Hamilton said, adding she urged the former student to also report to proper authorities.

Hamilton said if the charges are true the teacher will not return to Stamford Public Schools. Watkins remains suspended.

Hamilton was not aware of any other issues with Watkins in the 10 years Watkins has been a teacher.

During the investigation, police said they also identified a second 15-year-old student who Watkins allegedly provided with marijuana. In a statement to police, the student said Watkins provided him with marijuana and rolling papers on numerous occasions and he smoked marijuana with her in her car during school hours on school grounds.